The following relates generally to memory devices, and more specifically to a hybrid memory including a ferroelectric random access memory (FeRAM) array and a dynamic random access memory (DRAM) array.
Memory devices are widely used to store information in various electronic devices such as computers, wireless communication devices, cameras, digital displays, and the like. Information is stored by programming different states of a memory device. For example, binary devices have two states, often denoted by a logic “1” or a logic “0.” In other systems, more than two states may be stored. To access the stored information, the electronic device may read, or sense, the stored state in the memory device. To store information, the electronic device may write, or program, the state in the memory device.
Various types of memory devices exist, including random access memory (RAM), read only memory (ROM), DRAM, synchronous dynamic RAM (SDRAM), FeRAM, magnetic RAM (MRAM), resistive RAM (RRAM), flash memory, and others. Memory devices may be volatile or non-volatile. Non-volatile memory, e.g., flash memory, can store data for extended periods of time even in the absence of an external power source. Volatile memory devices, e.g., DRAM, may lose their stored state over time unless they are periodically refreshed by an external power source. A binary memory device may, for example, include a charged or discharged capacitor. A charged capacitor may become discharged over time through leakage currents, resulting in the loss of the stored information. Certain aspects of volatile memory may offer performance advantages, such as faster read or write speeds, while aspects of non-volatile, such as the ability to store data without periodic refreshing, may be advantageous.
In some cases, a FeRAM may be operated at a speed and with a nonvolatile property similar to that of a DRAM. In these cases, however, the ferroelectric capacitors used in the memory cells of the FeRAM may suffer from fatigue as a result of repeated polarizations and inversions of the ferroelectric materials within the ferroelectric capacitors, resulting in a reduction of residual polarization. Also, when writing operations are continuously carried out in the same polarization direction, a shift in the hysteresis characteristic of a memory cell, referred to as an “in-print,” may cause subsequent degradation in the rewriting characteristic of the memory cell. Compared to a DRAM, a FeRAM may therefore support fewer read-out and writing operations over its lifetime.
On the other hand, the ferroelectric capacitor of a FeRAM has a characteristic in which the ferroelectric characteristic by a residual polarization component and the paraelectric characteristic by a normal capacitor component are combined with each other, and by using only the paraelectric characteristic, without carrying out polarization inversion, the FeRAM may be operated similarly to a DRAM.